The present invention generally relates to a sensor for detecting red blood cells in plasma by comparing the absorption of red light and blue light directed through the plasma.
Blood generally consists of red and white blood cells suspended in plasma. Red blood cells find widespread use for making up serious blood losses as may be incurred during operations or as a result of injury. In order to assure adequate blood supplies for such contingencies, hospital blood banks and the military store red blood cells. In the process for separating red blood cells from plasma and other blood products, blood is typically placed in a flexible bag that is spun in a centrifuge. After being centrifuged, the red blood cells, white blood cells, and plasma are grouped in layers. The plasma and white blood cells have a lower density than the red blood cells so the white blood cells and plasma collect in layers above the red blood cells that are at the bottom of the bag. The bag then is squeezed so that the white blood cells and plasma are "expressed" out of the bag whereupon mainly red blood cells remain. Such separation currently is done under human supervision. When the operator observes red blood cells at a certain point in the bag, the operator stops the process. The result is a donor bag containing red blood cells with a small amount of plasma, and red blood cell free plasma in a second bag. The red blood cells may then be stored for near term use or prepared for cryopreservation for long term storage and later use.
It is standard blood bank procedure to separate red blood cells from plasma. Such separation makes available to the patient only those blood components required, whether it is the oxygen transport provided by the red blood cells, or the volume effects provided by the plasma. Red blood cells carry antibodies that may cause transfusion reactions in patients not properly cross-matched. Plasma from several donors is typically administered to a single patient. Foreign red blood cells may result in harmful hemolytic transfusion reactions such as hemolysis, anaphyltic reactions, urtcaria, noncardic pulmonary edema, hepatitis, and alloimmunization to red blood cell or white blood cell antigens, platelets or plasma proteins, etc. Thus, it is not desirable for plasma to contain red blood cells. Therefore, it is important that red blood cells plasma be separated as much as possible from plasma.